Hi All-
On the strength of the above advice I just got a quaddoubler (arrived UPS last night). Popped open my totally stock (well, I do have Oxypatcher running, and Fblit too) A4000, stuck quaddoubler on the daughterboard (the "b" model hangs off the side where there is room for it, something I was worried about!) and put everything back together easier than puting in a new ROM. It booted right up just fine. AIBB tests show it to be mostly 2.02 times faster than a stock A4000/40. Exceptions: drawing the beachball is 3 or 5 times as fast (oxypatch effect?), memory test is still stock speed (half as fast as a A3000). Some of the tests were only 1.5-1.8 times faster, I presume ones that had a memory component.
Subjectively, the GUI was faster, the icons just popped into the windows. I tried playing a few games and they all seemed to work, although megaball developed an odd lock up that needed a re-boot to get out of. Breathless seemed to look smooth at screen sizes I had found unusable before (I didn't try above 320-200 as that seemed to get a little jumpy). Genesis (the old fractal scenery generator from years ago) painted scenes fast enough to be fun again, which made me smile since that was my main reason to spend the $$ on a speed-up.
My major disappointment is that when I tried to play avi files on my OS3.9 Action tool, they looked slower and rougher than a plain vanilla 68040/25 system. (Anyone have a suggestion here?)
I spent $117 (with shipping) to almost painlessly double the speed of my system. I read somewhere that you should never upgrade less that 4 times speed, however the next plug and play step up for me would be some kind of 060 card at a much steeper cost. $100 now and then seems right to spend on a beloved old hobby computer.
Yours-
CRL :-)